Method for influencing the electrical power of a load with a pulse width modulated signal

ABSTRACT

A method is proposed for influencing the electrical power of a load with the assistance of a pulse-width modulated signal, the latter including the requirement of a continuous turn-on signal. The method provides that the continuous turn-on signal is terminated by an interrupt signal and that the continuous turn-on signal is followed by a clock-pulse phase having at least one fundamental period duration of the pulse-width modulated signal, the period including a turn-off time. The occasional interruption of the pulse-width modulated signal, which is present as the continuous turn-on signal, makes it possible to detect an operational quantity of the load that only arises during a power change in the load.

BACKGROUND INFORMATION

The present invention relates to a method for influencing the electricalpower of a load with the assistance of a pulse-width modulated signal.From the textbook by L. Retzbach, “Speed Controllers,” Neckar PrintingHouse, Villingen-Schwenningen, 2nd edition, 1982, a method is describedfor influencing the electrical power of DC-current electromotors withthe assistance of a pulse-width modulated signal. On pages 21-24, aprinciple of speed regulation is described that includes a pulse-widthmodulator. A comparator designated as modulator compares a DC voltage,which is a measure for the setpoint value of the electrical power of theDC-electromotor, with an AC voltage, which supplies a sawtooth voltagegenerator. The time during which the DC voltage exceeds the AC voltagesignal, determines, for example, the turn-on time. The duration of thefundamental period of the generated pulse-width modulated signal is setby the fundamental frequency of the sawtooth voltage generator. In thegeneration of the pulse-width modulated signal, two limiting cases canarise that are not described in greater detail in the cited literature.The limiting cases arise when the DC voltage consistently lies beneathor above the sawtooth-shaped voltage made available by the generator. Inone operational case, no further turn-on times occur. The electromotoris then no longer supplied with current. In the other operational case,the pulse-width modulated signal changes into a continuous turn-onsignal, so that the electromotor continually is fully supplied withcurrent.

Protection of the electromotor against overloading and of theoutput-stage circuit against the occurrence of an overcurrent isprovided by the motor current detector described on pages 83 and 84. Oneimplementation provides for the evaluation of the voltage drop occurringon the contact-break distance of the output-stage switch during theturn-on time.

SUMMARY OF THE INVENTION

The present invention is based on the objective of indicating a methodfor influencing the electrical power of a load with the assistance of apulse-width modulated signal, the latter including the requirement of acontinuous turn-on signal, which makes possible the detection of anoperational quantity of the load.

The method according to the present invention has the advantage that instipulating a continuous turn-on signal, which can arise as a limitingcase in response to a pulse-width modulated signal, an operationalquantity of the load can be detected that can only be detected throughan at least short-duration change in the electrical power supplied tothe load. An operational quantity of this type is, for example, acurrent change that arises in response to a change in the electricalpower fed to the load.

In this regard, the present invention provides that the continuousturn-on signal is terminated using an interrupt signal and that thecontinuous turn-on signal is followed by a clock-pulse phase having atleast a fundamental period duration of the pulse-width modulated signal,the period including a turn-off time.

The method according to the present invention has the advantage that, onthe one hand, the load, in the context of the influencing of theelectrical power with the assistance of a pulse-width modulated signal,can be provided with at least approximately full power and, on the otherhand, a change in the electrical power of at least short durationarises, the short-duration change being able to be used, for example,for detecting an operational quantity of the load.

A particularly advantageous embodiment of the method according to thepresent invention provides that a program-controlled signal-processingarrangement, which preferably generates the pulse-width modulatedsignal, generates the interrupt signal after one program cycle. Usingthis measure, a simple realization of the program flow sequence isachieved. In particular, the advantage arises that the program runningin the signal-processing arrangement brings to bear an influence on theelectrical power of the load, upon the generation of the interruptsignal, at exactly the moment at which the program of thesignal-processing arrangement expects the effects of the power change.In this manner, an unnecessary halt in the ongoing program flow isavoided.

Another advantageous embodiment provides that the interrupt signalarises due to an external request signal. On the basis of this measure,a controlled termination of a continuous turn-on signal is possible, theexternal request signal being preferably generated by the arrangementwhich detects the operational quantity of the load.

Further advantageous embodiments provide that the duration of theclock-pulse phase, which follows the continuous turn-on signal, amountsto a whole-number multiple of the fundamental period duration of thepulse-width modulated signal.

The method according to the present invention makes possible thedetecting of a measuring quantity in the area of the turn-off time,which arises during the clock-pulse phase. A measuring quantity of thistype is, for example, a change in the current flowing through the load.The current change, at an inductive component located in the circuit,for example, at an inductance-susceptible printed circuit trace of aprinted circuit, leads to an inductive voltage drop which isproportional to the current change. Using an integrator, the absolutecurrent can be inferred from the current change.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a block diagram of a circuit, in which the method accordingto the present invention is operating.

FIG. 2 shows a segment of a flowchart.

FIG. 3 shows a signal flow pattern assuming the requirement of acontinuous turn-on signal.

FIG. 4 shows a time-extended segment of the signal flow pattern depictedin FIG. 3.

DETAILED DESCRIPTION

FIG. 1 depicts a load 10, which is supplied from an energy source 11.Load 10 can be connected to energy source 11 via a switch 12. Switch 12is driven by a pulse-width modulated signal 13, which is generated by asignal-processing arrangement 14 as a function of a power default signal15 and a power limiting signal 16. Power limiting signal 16 is madeavailable by a current detector 17, which detects current I flowingthrough switch 12 and through load 10. The current detector evaluates aninduced voltage Ui, which arises at an inductive element 18, throughwhich current I flows. Current detector 17 also delivers a firstinterrupt signal U1 to signal-processing arrangement 14.

The following method can be realized on the basis of the block diagramdepicted in FIG. 1.

Signal-processing arrangement 14, which is preferablyprogram-controlled, generates pulse-width modulated signal 13 as afunction of power default signal 15, pulse-width modulated signal 13either completely switching on or switching off switch 12 in temporalsequence. Pulse-width modulated signal 13 makes available to load 10 anaverage voltage via switch 12, the voltage being applied from energysource 11. A change in the average voltage made available to load 10 hasan effect on average current I flowing through load 10. Pulse-widthmodulated signal 13, therefore, makes possible to influence theelectrical power supplied to load 10. If load 10, for example, is anelectromotor, then, using pulse-width modulated signal 13, the speed,for example, can be kept constant at a prescribed value. The detectionof the motor current, alternatively, makes it possible to keep constantthe torque generated by the electromotor.

The greatest possible power of load 10 arises when switch 12 iscontinuously turned on by pulse-width modulated signal 13. A continuousturn-on signal of this type, just as a complete turn-off signal, is aspecial case of pulse-width modulated signal 13. A complete supply ofcurrent to load 10, set for an unspecified time, is not possible in allcases. The case of this type arises if an operational quantity of load10 is to be detected, at which power shows a change at least of shortduration. Current detector 17 evaluates an inductive voltage drop Ui,which arises at inductive element 18. The inductive coating of a linecarrying current I can be used. A line printed on a printed circuittrace, for example, has sufficient inductance. Induced voltage Ui isproportional to the inductance and to the leakance of current I overtime. An integrator contained in the current detector, summing up thecurrent changes, makes available a signal that is proportional tocurrent I. Through a comparison with a preselected threshold value,power limiting signal 16 can be supplied to signal-processingarrangement 14. Power limiting signal 16 signals the presence of anovercurrent and causes signal-processing arrangement 14 to changepulse-width modulated signal 13 right up to entirely turning off load10.

The power change provided at least for short duration in response to anexisting continuous turn-on signal of pulse-width modulated signal 13 ispossible according to the present invention as a result of the fact thatthe continuous turn-on signal is terminated using an interrupt signaland that the continuous turn-on signal is followed by a clock-pulsephase having a least one fundamental period duration including aturn-off time. The interrupt signal, for example, is made available bycurrent detector 17 as external interrupt signal U1.

FIG. 2, in the context of a flowchart, depicts a different possibilityfor making available the interrupt signal. The interrupt signal arisesupon completing a program, which can run, for example, withinsignal-processing arrangement 14. The program begins with start 21 andproceeds via instructions 22 and queries 23 to instruction 24 at the endof the program, instruction 24 generating a program-generated interruptsignal U2. After instruction 24, a return to start 21 takes place.Pulse-width modulated signal 13 itself can also be generated in thecontext of the flowchart depicted in FIG. 2. The advantage of realizingprogram-controlled interrupt signal U2 lies in that program-controlledinterrupt signal U2 is made available within the normal programsequence. Intervening in the program, which is necessary in externalinterrupt signal U1, can be dispensed with.

The effect of the method according to the present invention on thepulse-width modulated signal is illustrated on the basis of the signalflow patterns depicted in FIGS. 3 and 4 as a function of time: FIG. 3depicts pulse-width modulated signal 13 as a function of time, theordinate marking “1” signifying that switch 12 is turned on, whereasmarking “0” signifies that switch 12 is turned off. Depicted is theoperating case in which pulse-width modulated signal 13 arises as acontinuous turn-on signal. According to the present invention, it isprovided that the continuous turn-on signal is terminated if aninterrupt signal U1, U2 arises. This is the case at time points Tu1,Tu2, Tu3. The interrupted continuous turn-on signal has a turn-onduration that is designated in FIG. 3 as Ted. Turn-on duration Ted isfollowed in each case by clock-pulse phases Tp.

FIG. 4 depicts a clock-pulse phase Tp having a time measure that isenlarged in comparison to FIG. 3. Within clock-pulse phase Tp, at leastone turn-off time Ta of pulse-width modulated signal 13 arises. Afterone turn-off period Ta, pulse-width modulated signal 13 can again betransformed into the continuous signal. Of the fundamental periodduration Tg entered in FIG. 4 of pulse-width modulated signal 13,composed of turn-off time Ta and turn-on time Te, only turn-off time Tawould be visible, since then turn-on time Te would already beattributable to the appearance of the continuous turn-on signal.Preferably, in clock-pulse phase Tp, a plurality of fundamental perioddurations Tg are contained. On the basis of this measure, the advantageis achieved that a sufficient change in the power made available to loadcan be realized without having to dispense with a comparativelyhigh-frequency clocking. Turn-off time Ta can therefore be maintained ata minimal constant value. A particularly simple realization, from theprogram-technical point of view, results if clock-pulse phase Tp is awhole-number multiple of fundamental period duration Tg.

What is claimed is:
 1. A device for influencing an electrical power of aload, comprising: a switch connected in series with the load; asignal-processing arrangement for driving the switch in accordance witha pulse-width modulated signal; a current detector in communication withthe signal-processing arrangement; and an inductive element arrangedwith respect to the current detector, wherein: the signal-processingarrangement generates the pulse-width modulated signal right up to acontinuous turn-on signal, in response to the continuous turn-on signal,the load is completely turned on, the current detector evaluates achange over time an induced voltage arising in the inductive elementthrough which a current flows, an interrupt signal is generated, and theinterrupt signal interrupts the continuous turn-on signal at least for aturn-off time of the pulse-width modulated signal.
 2. The deviceaccording to claim 1, wherein: the interrupt signal is made available bya program that runs in the signal-processing arrangement.
 3. The deviceaccording to claim 1, wherein: the interrupt signal is an externalsignal.
 4. The device according to claim 1, wherein: the evaluation ofthe induced voltage is accomplished during the turn-off time of thepulse-width modulated signal.
 5. The device according to claim 1,wherein the change over time in the induced voltage is a drop in theinduced voltage.
 6. The device according to claim 1, wherein the currentdetector includes an integrator, the integrator determining currentchanges.
 7. The device according to claim 1, wherein the currentdetector is configured to provide a power limiting signal to the signalprocessing arrangement as a function of the evaluation.
 8. The deviceaccording to claim 7, wherein the power limiting signal signals apresence of an overcurrent.
 9. A device for influencing an electricalpower of a load, comprising: a switch connected in series with the load;a signal-processing arrangement for driving the switch in accordancewith a pulse-width modulated signal; a current detector in communicationwith the signal-processing arrangement; and an inductive elementarranged with respect to the current detector, wherein: thesignal-processing arrangement generates the pulse-width modulated signalright up to a continuous turn-on signal, in response to the continuousturn-on signal, the load is completely turned on, the current detectorevaluates an induced voltage arising in the inductive element throughwhich a current flows, an interrupt signal is generated, the interruptsignal interrupts the continuous turn-on signal at least for a turn-offtime of the pulse-width modulated signal, the interrupt signal is madeavailable by a program that runs in the signal-processing arrangement,and the interrupt signal is generated after each program cycle.
 10. Adevice for influencing an electrical power of a load, comprising: aswitch connected in series with the load; a signal-processingarrangement for driving the switch in accordance with a pulse-widthmodulated signal; a current detector in communication with thesignal-processing arrangement; and an inductive element arranged withrespect to the current detector, wherein: the signal-processingarrangement generates the pulse-width modulated signal right up to acontinuous turn-on signal, in response to the continuous turn-on signal,the load is completely turned on, the current detector evaluates aninduced voltage arising in the inductive element through which a currentflows, an interrupt signal is generated, the interrupt signal interruptsthe continuous turn-on signal at least for a turn-off time of thepulse-width modulated signal, and the interrupt signal interrupts thecontinuous turn-on signal for a duration of a clock-pulse phasecorresponding to a whole-number multiple of a fundamental periodduration of the pulse-width modulated signal.
 11. A device forinfluencing an electrical power of a load, comprising: a switchconnected in series with the load; a signal-processing arrangement fordriving the switch in accordance with a pulse-width modulated signal; acurrent detector in communication with the signal-processingarrangement; and an inductive element arranged with respect to thecurrent detector, wherein: the signal-processing arrangement generatesthe pulse-width modulated signal right up to a continuous turn-onsignal, in response to the continuous turn-on signal, the load iscompletely turned on, the current detector evaluates an induced voltagearising in the inductive element through which a current flows, aninterrupt signal is generated, the interrupt signal interrupts thecontinuous turn-on signal at least for a turn-off time of thepulse-width modulated signal, and the inductive element corresponds to aprinted circuit trace arranged on a printed circuit.